Various articles are assembled from more than one material, forming multiple portions of the article. In general, such articles are formed by securing a first material to a second material using a securing technique such as welding, adhering, fusing, soldering, brazing or a combination thereof. Such techniques suffer from various drawbacks. For example, such techniques can suffer from limited applicability to alloys, can be subject to fatigue, can delaminate, or combinations thereof.
Articles formed from combined alloys are often used in power generation systems, engines, bridges, buildings, wind turbines, and other large structures. Such structures are continuously subjected to increasing forces to provide improved efficiency and/or due to new environmental conditions. Such articles require increased resistance to fatigue, increased mechanical properties, increased capability of being fabricating, increased design life and reduced life cycle cost. Known components having two or more materials do not sufficiently meet all of the desired parameters.
As an alloy ingot cools, there are many factors which affect the final structure of the article formed. For example, when a molten alloy is poured into a mold, a temperature difference between the mold and the alloy causes thermal convection currents at the mold wall. The convection current contributes to segregation and the breaking off of metal dendrites forming on the wall. Those dendrites act as nuclei for the formation of equiaxed grains. Changing local compositions contributes to segregation, which further complicates grain formation. Additionally, the composition of the alloy and the rate at which the cast cools affect the final grain structure. Known casting methods do not sufficiently address such concerns regarding grain formation.
A casting method, a cast article, and a casting system that do not suffer from one or more of the above drawbacks would be desirable in the art.